Information storage and/or retrieval systems which have optical disk drives and any type of optical disk for the storage and/or retrieval of information use optical scanners for directing a laser beam or beam of light to an objective lens near the optical disk. The laser beam is used for reading information from or writing information on the disk. Optical scanners typically include a moving iron galvanometer which is used to rotate a mirror which in turn deflects the laser beam through an objective lens to the surface of an optical disk. A position transducer detects the angle of deflection of the mirror to indicate the location of the laser beam when positioned over the information tracks on the disk. In this manner, the laser beam can be accurately directed to the desired tracks of information on the surface of the disk.
One way to achieve tracking position is to direct the beam of light to the surface of the optical disk, receive the reflected light from the disk, and return the reflected beam of light to a control system which monitors the beam of light to sense tracking of the laser beam, thereby controlling the position of the optical scanner. Another method involves monitoring a feedback signal from a position transducer which senses the position of the mirror which deflects the laser beam.
Known galvanometer devices and methods use a moving coil or a moving vane and are usually big and bulky in physical size. Such devices are of a complex construction and have a poor low frequency response due to the large inertia resulting from the size of the moving parts. Because of their generally large size, these devices consume large amounts of power. In general, these known galvanometer devices employ two or more large permanent magnets which are contained within a stator. A rotor is mounted to rotate within the stator under the influence of magnetic flux which is developed by current flowing in coils. Mechanical return springs or torsion bars are used to return the rotor of these devices to a neutral position when no current is flowing in the coils. The use of mechanical springs or torsion bars introduces a resonance frequency problem which is undesirable in the servo control system.
Prior art devices, due to their comparatively large size, do not adequately provide the desired response time necessary to operate the optical disk system as efficiently as possible. In addition, the mechanical spring or torsion bar introduces low frequency resonance problems which reduce the accuracy of the positioning of the mirror.